As an extension work of computer codes QUEN1D, KREWET and BEAR developed by previous workers at KAIST has been performed. This study is based on a signle flow channel, and separated two phase flow. The heat transfer selection logic is developed and the heat transfer coefficients are calculated as a function of the local flow conditions. The wall temperataure history is calculated by solving the time-dependent radial conduction equation. Comparison between predictions and PWR-FLECHT experiment data shows a relatively good agreement, but further improvement seems to be necessary for low pressure and low flloding rate conditions.